Rotational molding (also commonly called rotomolding) is a method of manufacture for primarily large, hollow or partial shell-shaped plastic objects. This process utilizes a shell mold having a cavity into which is placed a powdered (optionally colored and sometimes liquid) plastic resin. The mold is then closed and placed in an oven where it is heated and rotated about one or more axes. Rotation of the mold can include either complete revolutions about two axes or complete revolutions about a single axis with partial revolutions about a second axis. In both cases, the two axes of rotation typically are mutually perpendicular. The heat causes the resin to melt against the heated inside surface of the mold. The melted resin flows within the cavity to form a viscous membrane conforming to the mold's inner surface. The mold (and the plastic inside) is then cooled while rotation continues, causing the resin to harden in the shape of the cavity.
In the past, multi-colored rotationally molded products typically would be formed by separately rotationally molding single color parts and then fastening the parts together to form an integral structure. Multi-colored products also have been rotationally molded in a single mold, particularly in the kayak industry. Rotational molding of two-color kayaks can be done because the molding process involves rotating the mold on only one axis, rather than two axes. The colors, however, are not clearly separated as there is some blending that occurs in the area where the different colors of pigmented resins mix in the mold.
Applicants' assignee also has rotationally molded two-color products, in particular two-color slides, about two rotational axes by controlling the rotation of the mold during the molding process. The two colors of pigmented resin, however, were blended.
While the blending of the colors may be desirable for some applications, for others it is not. In these latter instances, the manufacturer would be left with molding the differently colored parts separately and then fastening them together to form the finished product.